Lecture Notes: Natural Selection and Evolutionary Changes

Introduction

• Speaker: Hank
• Main Idea: Explanation of natural selection using the example of the peppered moth during the Industrial Revolution.

Peppered Moth Example

• Early 1800s London: Light-colored moths blend in with lichens and tree bark.
• Impact of Industrial Revolution: Factories emit soot, darkening environment, leading to increased visibility of light moths to predators.
• Result: Dark moths (initially 2% of population) thrive, reaching 95% by 1895 due to better camouflage.
• Concept: This is an example of natural selection, a process identified by Charles Darwin.

Natural Selection Principles

• Principle 1: Individual variations exist within a population (phenotypes).
• Principle 2: Many variations are heritable (genotype).
• Principle 3: Populations often produce more offspring than resources can support (struggle for existence).
• Principle 4: Heritable traits affecting fitness lead to variations in survival and reproduction rates.

Darwin and His Observations

• HMS Beagle Voyage: Observed adaptations on Galapagos Islands, notably finches with different beak shapes.
• Adaptations: Traits enhancing survival and reproduction in specific environments.
• Fitness: Relative ability to survive and produce offspring.

Evolutionary Mechanisms Beyond Natural Selection

• Mutation, Migration, Genetic Drift: Other factors influencing evolutionary change.

Modes of Selection

• Directional Selection: Favored trait is at one extreme (e.g., peppered moths, giraffe necks).
• Stabilizing Selection: Favors majority well-adapted traits (e.g., human birth weight).
• Disruptive Selection: Favors extreme traits at both ends, rare but observed in Daphnia crustaceans.

Sexual Selection

• Introduced by Darwin, focusing on traits that enhance mating success.
  • Attractiveness (e.g., peacock tails): Directional sexual selection.
  • Intimidation/Fighting: Selection for stronger individuals.

Artificial Selection

• Humans select traits in plants and animals (e.g., domesticating dogs, breeding plants).

Conclusion

• Key Concept: Natural selection changes genetic composition of populations, not individuals.
• Upcoming Topic: How species differentiation occurs.

Discussion

• Encouragement for questions and further exploration on social media channels.

Key Terms:

• Natural Selection: Process by which traits that enhance survival and reproduction increase in frequency in a population.
• Phenotype: Observable traits of an organism.
• Genotype: Genetic makeup of an organism.
• Fitness: Ability to survive and reproduce.
• Directional, Stabilizing, Disruptive Selection: Types of natural selection based on trait favorability.
• Sexual Selection: Selection based on mating success.
• Artificial Selection: Human-driven selection of traits.